Pyrite trace element and S-Pb isotopic evidence for contrasting sources of metals and ligands during superimposed hydrothermal events in the Dongping gold deposit, North China

The Dongping gold deposit, located near the northern margin of the North China Craton, contains ore bodies spatially associated with the Devonian Shuiquangou syenite, Cretaceous Shangshuiquan granite, and Archean metamorphic rocks. Major and trace elements and S-Pb isotopes of pyrite from two stages of gold-quartz veins and wall rocks were used to constrain the composition of hydrothermal fluids and metal sources. Stage-1 (early) pyrites are euhedral to subhedral, medium- to coarse-grained, and have low gold contents. Py1a is homogeneous with few fractures, whereas Py1b, which occurs on the edges of Py1a, is porous and has higher metal contents. Stage-2 (late) pyrites are mostly anhedral to subhedral and have smaller grain sizes and higher gold contents than Stage 1. Py2a occurs with sulfide minerals such as galena and chalcopyrite, and Py2b is porous and has the highest gold content (up to 1839 ppm) and smallest grain size. All pyrite samples yield negative 5 34 S values (- 7.5 to - 3.5%c), reflecting oxidized conditions during mineralization. The similar to 2% decrease in delta S-34 values from Stage 1 (-4.3 parts per thousand, - 4.9 parts per thousand) to Stage 2 (- 7.0 parts per thousand, - 6.4 parts per thousand) may reflect a change in the fluid source and/or an increase in . fO(2) . The Pb isotope composition of Stage-1 pyrite is suggestive of a mantle source similar to that of the Shuiquangou syenite, whereas Stage-2 pyrite has more radiogenic Pb isotopic compositions suggestive of an Archean metamorphic source. Combined with previous studies, our trace element and isotopic results indicate that the two stages of pyrite had different sources, with Stage-2 pyrite being more strongly influenced by metasedimentary rocks. We propose that the early stage of low-grade gold mineralization was related to emplacement of the Devonian Shuiquangou syenite, whereas the late stage of high-grade gold mineralization was related to emplacement of the Cretaceous Shangshuiquan granite and leaching of gold from Archean metamorphic rocks.

Automated summary

By studying the chemistry and isotopes of pyrite, we have revealed that the two stages of pyrite in the Dongping gold deposit have different metal sources, with the later stage being more influenced by metasedimentary rocks and the earlier stage being more influenced by the syenite.